fix diskstats_show() accounting with PREEMPT

PATCH In review Ingo Molnar 2 participants 2 messages Sep 21, 2004 – Sep 22, 2004 Block layer

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Ingo Molnar

author

2004-09-21 15:36 UTC #0 lore raw

PATCH 1/1 fix diskstats_show() accounting with PREEMPT

there is another (minor) bug that the smp_processor_id() debugger
unearthed: diskstats_show() could do a disk_round_stats() -> disk_stat_add() with preemption enabled - possibly resulting in losing statistics updates.

Patch attached. (The overwhelming majority of disk_stat_add() callers have preemption disabled so fixing the remaining two was the best.)

Ingo

Signed-off-by Ingo Molnar <[email protected]>

drivers/block/genhd.c renamed from drivers/block/genhd.c.orig +4 -0

@@ -365,7 +365,9 @@ static ssize_t disk_size_read(struct gen
 
 static ssize_t disk_stats_read(struct gendisk * disk, char *page)
 {
+	preempt_disable();
 	disk_round_stats(disk);
+	preempt_enable();
 	return sprintf(page,
 		"%8u %8u %8llu %8u "
 		"%8u %8u %8llu %8u "

@@ -494,7 +496,9 @@ static int diskstats_show(struct seq_fil
 				"\n\n");
 	*/
  
+	preempt_disable();
 	disk_round_stats(gp);
+	preempt_enable();
 	seq_printf(s, "%4d %4d %s %u %u %llu %u %u %u %llu %u %u %u %u\n",
 		gp->major, n + gp->first_minor, disk_name(gp, n, buf),
 		disk_stat_read(gp, reads), disk_stat_read(gp, read_merges),

Jens Axboe

2004-09-22 10:57 UTC #1 lore raw

Quoted 26 lines · Ingo Molnar

there is another (minor) bug that the smp_processor_id() debugger
unearthed: diskstats_show() could do a disk_round_stats() -> disk_stat_add() with preemption enabled - possibly resulting in losing statistics updates.
Patch attached. (The overwhelming majority of disk_stat_add() callers have preemption disabled so fixing the remaining two was the best.)
Ingo
Signed-off-by Ingo Molnar <[email protected]>
drivers/block/genhd.c renamed from drivers/block/genhd.c.orig +2 -0
@@ -365,7 +365,9 @@ static ssize_t disk_size_read(struct gen
 
 static ssize_t disk_stats_read(struct gendisk * disk, char *page)
 {
+	preempt_disable();
 	disk_round_stats(disk);
+	preempt_enable();
 	return sprintf(page,
 		"%8u %8u %8llu %8u "
 		"%8u %8u %8llu %8u "

drivers/block/genhd.c static int diskstats_show(struct seq_fil · line 504

Quoted 9 lines

drivers/block/genhd.c renamed from drivers/block/genhd.c.orig +2 -0

@@ -494,7 +496,9 @@ static int diskstats_show(struct seq_fil
 				"\n\n");
 	*/
 
+	preempt_disable();
 	disk_round_stats(gp);
+	preempt_enable();
 	seq_printf(s, "%4d %4d %s %u %u %llu %u %u %u %llu %u %u %u %u\n",
 		gp->major, n + gp->first_minor, disk_name(gp, n, buf),
 		disk_stat_read(gp, reads), disk_stat_read(gp, read_merges),

Looks fine, thanks Ingo.

Signature · 1 line

Jens Axboe